Increased virulence of human pandemic strains is associated with the introduction of avian influenza virus (AIV) genes into human viruses, and infection by highly pathogenic influenza strains is associated with acute pulmonary edema which enhances viral pathogenesis. The molecular mechanisms that direct increased alveolar fluid accumulation during infection are currently unknown and defining virulence factors in highly pathogenic human influenza viruses is crucial for developing therapeutics that stems the severity of future pandemics. We have shown that only AIV NS1 PLs bind specifically to the PDZ domain of the Kv1.4, a potassium channel that regulates alveolar fluid accumulation, and to Scribble, a regulatory protein that directs channels to apical membranes and mediates tight junction (TJ) formation. The Kv1.4 potassium channel contains both an N-terminal PDZ domain and a C-terminal PL motif and PL interactions regulate Kv1.4 apical membrane localization and function. Kv1.4 regulates alveolar fluid accumulation by pumping potassium into the alveolar space and concomitantly directing fluid resorption from the alveolus. Preventing potassium channel function reportedly causes the accumulation of alveolar fluid and pulmonary edema ( ). The PL motif of Kv1.4 is nearly identical to PLs present in AIV NS1s and is a consensus PDZ ligand for 2 PDZ domains of Scribble. Scribble is a scaffolding protein containing 4 PDZ domains which regulates apical membrane localization of integral membrane proteins and Rho directed permeability of tight junctions. We hypothesize that the NS1 PLs of highly pathogenic influenza viruses compete for PL binding sites on Kv1.4 and Scribble, blocking alveolar fluid resorptive functions of Kv1.4 and uncoupling tight junction assembly which results in enhanced accumulation of fluid in alveoli. Objective: In this proposal we will determine whether the PL from highly pathogenic AIV strains block Kv1.4 function and alter tight junction protein assembly which increases pulmonary fluid accumulation. These studies address a specific means for influenza viruses to direct fluid accumulation within alveoli and enhance the pathogenesis of pandemic strains. Proposed studies will define a potential influenza virulence determinant, identify targets for therapeutically regulating the pathogenesis of future pandemic influenza viruses and provide a rationale for using existing potassium channel activators to reduce fluid accumulation in the lung during infection. Increased virulence of human pandemic strains is associated with the introduction of avian influenza virus (AIV) genes into human viruses, and infection by highly pathogenic influenza strains is associated with fluid accumulation in the lung which enhances disease and the lethal outcome of infection. Proposed studies address a specific means for influenza viruses to direct fluid accumulation within the lung and increase the severity of disease caused by pandemic influenza viruses. Results will provide a means for using drugs to regulate influenza disease severity during future pandemics and rationales for evaluating existing drugs (that activate potassium channels) for their ability to reduce fluid accumulation in the lung during influenza virus infection. [unreadable] [unreadable] [unreadable]